In the field of engineering machinery, the crane is a commonly used hoisting engineering machinery related equipment. With continuous progress of technology, the crane develops rapidly toward a direction of lightweight and intelligence, so that it is necessary to require technical staff to uphold the design concept of lightweight at all times in the design process. As one of the core components of the crane, the hydraulic system is required to be as concise as possible, and the elements in use to be in less amount and light weight.
The hydraulic system of the crane is functionally divided into an upper part hydraulic system and an lower part hydraulic system. The upper part hydraulic system, which is mainly used during operation of the crane, comprises a luffing system, a telescopic system, a winch system, a revolving system, an auxiliary system and so on; the lower part hydraulic system, which is mainly used in a running state, comprises an outrigger system, a suspension system, a steering system, a cooling system and so on.
The hydraulic system of the crane is principally divided into an open system and a closed system. The oil passage of the open system is in a way such that a hydraulic pump sucks oil from an oil tank and reaches an actuation element via a control valve, and oil discharged by the actuation element returns to the oil tank in which the oil may be cooled, and the open system is a common manner of a hydraulic system. The oil passage of the closed system is in a way such that a hydraulic pump inputs oil into an oil inlet of the actuating element, and oil discharged from the actuating element is directly supplied to an oil suction port of the hydraulic pump. A variable displacement pump is used for changing a direction. Although the circuit mechanism is compact, the cooling condition is poor so that it is necessary to provide an oil supplementing circuit to supplement leakage in the circuit. A crane below a hundred-tonnage level mainly use an open system, i.e. one or more main pumps for telescoping, luffing, winching, and revolving system actions. The products of above a hundred-tonnage level mainly use a coexistent manner of an open system and a closed system, in which the open system is mainly used in telescopic, luffing and auxiliary circuits, while the closed system is applied in a revolving system and a winch system (including a main winch system, a secondary winch system, and a tower arm winch system). However, the closed system is generally in a way such that a pump corresponds to an action, thus resulting in a large amount of pumps in the entire hydraulic system. Take a crane of some tonnage for instance, the upper part hydraulic system has as many as nine pumps.
The existing winch and revolving systems of a crane, which are shown in FIG. 1, respectively use an independent closed system. Among them, in order to ensure that the winch system has a wider speed governing range, most of the winch motors are variable displacement motors, while the revolving system needs to have a better micro-movement, the revolving motor mainly is a constant displacement motor. In FIG. 1, a1 and a2 are closed pumps, a3 is a winch motor, a4 is a revolving motor, a5 and a6 are both brakes, a7 is a brake control valve, a8 is a buffer valve, a9 is a slip valve. The closed pump a1 directly drives the winch motor a3 to effectuate an action of the secondary winch (tower arm winch) and the closed pump a1 does not participate in operation of other systems. The closed pump a2 alone directly drives the revolving motor a4, so as to achieve a revolving action, and the closed pump a2 likewise does not participate in operation of other systems.
Thus, the existing hydraulic systems of a crane are at least present with the following technical defects:
(1) Revolving and secondary winch (tower arm winch) are driven respectively using different pumps so that the pumps are in large amount and great volume, which results in heavy weight of complete vehicle.
(2) The pumps at a pump set are in large amount, the pipeline of the pump set accessory is subjected to a great connection difficulty, and the connection pipeline is complicated, which results in high cost of the hydraulic systems.